The pressor effect of angiotensin II was studied in one patient during hypokalemic and normokalemic states. With hypokalemia, the pressor dose required was 200 ng/kg/min. When serum K was restored to normal the pressor dose dropped down to 30 ng/kg/min., suggesting that hypokalemia may result in vascular hyporesponsiveness in patients with hypokalemia of idverse origin.